Hi @hmafzal,
This could be solved in many ways, it is on the logic that you want to get your string converted to a list of elements.
If you are sure that every time your input is going to within { } then you could trim that off in your java service, just like this input = input.substring(1, input.length()-1);
Try and let me know if it works as per your expectation.
Thanks,
Sree